[Racket announcement] Racket v6.10

Racket version 6.10 is now available from

    http://racket-lang.org/

Note: Graphical Racket programs such as DrRacket are affected by a bug
in the Windows 10 Creators update which can lead to blue screens and
require reboots. We are aware of the issue, and have mitigated it in
DrRacket, which reduces the incidence of crashes. Microsoft has
diagnosed the issue and will release a fix in a future Windows update.
Additional details are available here:
    https://github.com/racket/racket/issues/1671

* Internally, Racket's intermediate compatibility layer over
  operating-system facilities has been moved into its own library,
  "rktio", so it can be used in future Racket implementations. This
  change should be transparent, but the refactoring moves code that
  has many compiler and OS dependencies, so we expect a new glitch or
  two in less-common build and execution environments. Please report
  problems at https://github.com/racket/racket/issues .

* Racket supports cross-compilation of executables in more cases,
  including executables that depend on packages for foreign libraries.

* The `struct` form supports an `#:authentic` annotation to declare
  that chaperones and impersonators are never allowed on instances of
  the declared structure type. This annotation is intended for use on
  a library's internal data structures, where it won't interfere with
  contracts or other forms of extension at a library's interface. It
  can sometimes provide a small performance boost.

* RackUnit adds `nested-info` and `string-info` to grant custom checks
  more control over the display and layout of check failure info.

* The `raco test` command provides the `++arg` and `++args` flags to
  pass arguments to tested programs.

* Typed Racket has types for immutable, mutable, and weak hashtables; in
  other words the type `(HashTable K V)` is a union `(U
  (Immutable-HashTable K V) (Mutable-HashTable K V) (Weak-HashTable K
  V))`. Standard library functions may have more specific return types.
  For example, `hash-set` has type `(-> (HashTable K V) K V
  (Immutable-HashTable K V))`.  When an immutable hashtable flows from
  untyped code to typed code, Typed Racket may use a flat contract to
  verify its type (provided the table's key and value types are flat).

* The Typed Racket Optimizer is disabled in untrusted contexts (e.g.,
  sandboxes). This prevents unsoundness in the Typed Racket type system
  from being used to get access to unsafe operations.

* Racket's internal runtime adds a `scheme_atexit` procedure with
  identical behavior as `atexit` defined in libc.

The following people contributed to this release:
Alex Knauth, Alexander McLin, Alexis King, Andrew Kent, Ben Greenman,
Ben Noordhuis, Carlo Dapor, Conor Finegan, Daniel Feltey, Ethan Estrada,
Georges Dupéron, Gary F. Baumgartner, Gianluca Ciccarelli, Gustavo
Massaccesi, Harold Carr, Jack Firth, Jay McCarthy, John Clements,
Kimball Germane, Leandro Facchinetti, Lehi Toskin, Leif Andersen,
Matthew Butterick, Matthew Flatt, Matthias Felleisen, Michael Orlitzky,
Milo Turner, Mohsen Keyhani, Philip McGrath, Robby Findler, Rob Bassi,
Ryan Culpepper, Sam Caldwell, Sam Tobin-Hochstadt, Scott Moore, Spencer
Florence, Stephen Chang, Stephen De Gabrielle, Vincent St-Amour, WarGrey
Gyoudmon Ju, and William J. Bowman.

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